The present invention relates to a circular, two-cylinder knitting machine, commonly denominated "links-links", for the production of tubular knitted fabrics, with plain stitches and purl orrib stitches, and with the possibility of programming a very wide range of different patterns.
A machine of this kind is normally equipped with a plurality of yarn feeds, so as to produce, at each machine revolution, a plurality of courses of knitted fabric, and thus increase the productivity.
For each yarn feed station or knitting station, it is necessary to suitably select the needles from one of three basic knitting positions, i.e., to cause that, for each needle, deciding is possible, whether the needle has to remain inoperative, whether it must operate in plain mode (on the lower cylinder), or in purl mode (on the upper cylinder), or whether it must hold the stitch in plain mode (the so-said "loaded position", wherein the needle takes the new yarn in plain mode, but without releasing the previously formed stitch, retaining it).
In order to perform this selection of the needles, a selection device is associated with each yarn feed station or knitting station, which is mechanically driven, or, in particular in modern machines, is electromechanically or electronically controlled, comprising a plurality of selection members capable of acting on pattern heels of suitable selectors inserted inside the peripheral slots of the lower cylinder of the machine under the needles, normally with the interposition, between the needles and the selectors, of the so-said "needle pushers". The heels of the selectors are positioned at several levels.
The axial movement of the needles inside the respective slots of the cylinders is driven, besides the selection devices, by stationary and movable cams located on skirts surrounding the cylinders.
These machines are furthermore provided with devices for regulating the length of the stitch, and, possibly, with devices, denominated "yarn selectors", associated with the individual yarn feeds, by means of which it is possible to selectively supply to each feed point one from a plurality of yarns of different colours or types. The yarns fed at each yarn feed come from bobbins or cones, supported by cone carriers.
In order to enable the needles to carry out inside the slots housing them, the axial movements, which are necessary for forming the stitch, it is essential to have a mutual revolutionary motion between the cylinders bearing the needles, and the members which select the needles and which cause this up-and-down movements, i.e., the cams provided in the skirts surrounding the cylinders. This mutual revolutionary motion can be obtained with the cylinders being stationary, and the cams and the selection devices being revolving, or with revolving cylinders, and stationary cams and selection devices.
In the multi-yarn-feed, double-cylinder circular knitting machines known from the prior art, resort was made to the first of these two possibilities, with stationary cylinders in the centre of the machine, and with the cam skirts and the selection devices revolving around the stationary cylinders together with the possible yarn selectors, the stitch length regulating devices, and, of course, the yarn feed cones.
This solution was adopted in order to be able to prearrange on one single control station, radially outside the cylinders of the machine, a mechanical control programmer, in order to drive, according to the processing requirements, the selection devices, the movable cams in the cam skirts, and the possible yarn selectors, and other devices. In fact, if the revolving cylinder solution had been adopted, it would have been necessary to have the cylinders revolve in synchronism with the cam control devices, the needle selection devices, the yarn selectors, and so forth, with self-explanatory, practically unsurmountable structural complications.
On the other hand, a machine having stationary cylinders would require various devices for the selection and the drive of the axial movements of the revolving needles with results clearly very complex and cumbersome, if one considers that the frame structure supporting the whole revolving portion of the machine must be very sturdy, and considering the tremendously large revolving mass subject to the centrifugal force, which also considerably limits the revolution speed, and therefore also the production rate of the machine. Furthermore, in a so-conceived machine, the actions for controlling and supervising the machine operation become extremely difficult and dangerous, by being hindered by the external revolving portion of the machine.
The technical problem on which the present invention is based, and for which a solution is proposed, is now that of providing a universal, double-cylinder, multi-yarn-feed circular knitting machine of novel conception, wherein the drawbacks of the machines of this kind known from the prior art are overcome, and installation of the needle drive cams, the needle selector devices, the possible yarn selector devices, the stitch length regolator devices, the yarn guides, the feed cones, and so forth is possible on the stationary structure provided around the revolving cylinders, with less complexity and overall dimensions, greater easeness of operation control and supervision, and possibility of higher revolution speeds, and, therefore, of a higher production rate.
In order to solve this problem, according to the present invention, it is proposed to use electromechanical actuators for driving the movable members destined to act on the needles of the cylinders and on the yarn feed means, with said members and means being installed on the stationary portion of the machine surrounding the revolving cylinders, and to send the actuation signals to said electromechanical drive actuators from a central electronic control unit in synchronism with the revolution of the cylinders, as a function of the pattern of the knitted fabric to be produced, as detected by a pattern analyzer, and processed by a computer.
By operating in this way, it is possible to keep the two revolving cylinders, and all of the drive members stationary, in as much as the signals of actuation for these drive elements are, at is were, made to "travel" at the same speed of the revolving cylinders.
According to a particularly preferred form of a practical embodiment of the present invention, each yarn feed of the machine is equipped with two successive groups of electromechanical selection actuators, such to be able to perform, for each yarn feed, in one single station, the three basic stitch selections, i.e., to select the needles which must remain inoperative in the relevant yarn feed, the needles which must operate in plain mode, or in purl mode, and the needles which must operate in the loaded position in the plain mode.
In this way, also the number of movable cams is decreased, because the machine can operate with only stationary cams associated with the lower cylinders, and with only two movable cams, also equipped with electromechanical actuators, associated with the upper cylinder.
Of course, also the possible yarn selector devices of the machine must be equipped with an electromechanical drive means, as per se known from the prior art.
With the solution provided by the present invention, the structure of the double-cylinder, multi-yarn-feed circular knitting machine is enormously simplified, the overall dimensions thereof are reduced, and the operation control is made easier, besides making it possible the production rate to be considerably increased, both due to the fact that the mass of the revolving part is largely reduced as compared to the machines of the same kind known from the prior art, so that it is possible to increase the revolution speed, and--in the preferred form of the practical embodiment--due to the fact that for each yarn feed, the three basic stitch selections can be carried out on one single station, and not any longer on three stations as it occurs in the prior art, so that it is possible to increase the number of the actually operating yarn feeds.